This invention relates to a photoreceptor method and assembly and, more particularly, to a photoreceptor method and assembly for use in a photocopy apparatus.
In photocopy apparatus, and particularly electrostatic copiers having either drum or belt photoreceptors, the maximum copy rate is usually limited by the time it takes to expose the photoreceptor to transfer the image which is to be copied to the photoreceptor. In recent belt photoreceptor apparatus flash exposure of the entire document to image the photoreceptor belt at the imaging station of the apparatus has resulted in substantial increases in copy rate over the prior scanning imaging methods and apparatus previously used. Although flash exposure increases the copy rate, the imaging phase of the copying process still constitutes the limit on the maximum copy rate of the machine. Moreover, flash exposure imaging suffers several disadvantages. One disadvantage is that flash exposure imaging requires light illumination intensities substantially greater than those in prior imaging systems. In addition, the photoreceptors employed in flash exposure imaging must be highly sensitive and held flat during exposure. Thus, only a narrow range of photosensitive materials may be used in such flash exposure systems and, thereby, other materials which have other advantageous physical and mechanical properties frequently can not be used.
In the method and assembly of the present invention, the photoreceptor may be stopped at the imaging station during the time that the image is being transferred to the photoreceptor, even though the photoreceptor continues to move at a constant speed through the processing stations. The ability to slow or stop the photoreceptor at the imaging station during imaging has several advantages. One advantage is that lower light intensities may be employed during imaging, flash or otherwise. Another advantage is that a wider range of photoreceptor materials may be employed. Thus, photoreceptor materials having optimum mechanical properties, e.g. crack resistance, abrasion resistance, good substrate adhesion, etc., may be selected without a reduction of given copy rate, even though the sensitivity of the photoreceptor is reduced. Conversely, for highly sensitive photoreceptors, the method and assembly of the present invention are capable of substantially improved copy rates, in fact, so improved, that the maximum copy rate limit is no longer governed by the imaging limitations. Another advantage of the method and apparatus of the present invention is the improved quality of the copy product. Even in flash exposure systems where image transfer is extremely rapid, the photoreceptor material will still move a small predetermined amount during the time of exposure due to the constant speed of the photoreceptor. This small amount of movement or displacement will cause at least some slight smearing. Conversely, in the photoreceptor assembly and method of the present invention, the photoreceptor may be brought to a complete stop during exposure preventing any such smearing.
In one principal aspect of the present invention, a photoreceptor system for a photocopying apparatus including a flexible endless photoreceptor means, a processing station, an imaging station for transferring the image to be copied to the photoreceptor means, and drive means for driving the photoreceptor means through the processing and imaging stations, includes velocity control means for controlling the velocity of the photoreceptor means such that the velocity at the processing station is substantially constant while the velocity at the imaging station may, simultaneously, be less than the substantially constant velocity.
In another principal aspect of the invention, the velocity control means comprises a movable shuttle means between the imaging and processing stations, whereby the photoreceptor means may be stopped during imaging at the imaging station and then rapidly removed from the imaging station upon completion of imaging.
In still another aspect of the present invention, a method of photocopying comprises driving flexible endless photoreceptor means through imaging and processing stations of a photocopy apparatus, moving the photoreceptor means at a velocity less than a given velocity at the imaging station while transferring the image thereto to be copied, and simultaneously moving the photoreceptor means at the given velocity through the processing station.
In still another principal aspect of the present invention, the velocity in the last mentioned process which is less than the given velocity is zero and the photoreceptor means may also be moved at the imaging station at a velocity greater than the given velocity after the image has been transferred thereto while simultaneously moving the photoreceptor means at the given velocity through the processing station.
These and other objects features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.